1. Field of the Invention
This invention relates to resin materials consisting essentially of radical polymers of ethylenically unsaturated monomers. More specifically, this invention relates to resin materials characterized mainly by the ethylenically unsaturated monomers to be polymerized into the resin materials.
Recently, various optical devices have been developed and remarkable developments are being achieved in the field of information processing. Some of such devices utilize discs (e.g., videodiscs, memory discs, and digital audiodiscs) for optically storing information therein.
For example, optical discs are expected to be widely used practically for recording and reproducing images and sounds, memory and reproduction of a large amount of information and the like because such optical discs exhibit many characteristics such as markedly high recording density and excellent images and sounds reproduced therefrom and the like.
2. Description of the Prior Art
The above mentioned discs are being produced from various materials. However, such materials have both merits and demerits, and it can be said that materials that are fully satisfactory for discs have not yet been proposed.
That is, for example, with respect to memory discs, inorganic glass and polymethylmethacrylate resin are practically used as the disc materials. Inorganic glass as a disc material, however, is disadvantageous in that it is heavy and fragile, costly for its precise processing and the like, although it is moisture-proof, and thus moisture has little adverse effects on a recording layer. On the other hand, polymethylmethacrylate resin materials are less fragile than the inorganic glass and are lower in cost, but have fatal defects as materials for optical devices in that they have low heat resistance and high hygroscopicity. Thus, the resulting discs warp so easily that an objective lens in a recording-reproducing optical system becomes out of focus owing to the warp and causes errors in operation.